Despite that, Afghanistan’s 15-year-old war grinds on with no clear victory in sight. Taliban fighters have been threatening at least two provincial capitals this summer, in Helmand and Kunduz, and a US government report said Afghan forces have lost 5% of territory this year.

Isis has been largely confined to a handful of districts in Afghanistan’s Nangarhar province – where Khan was killed – which borders Pakistan. Isis militants – mostly defectors from the Taliban – are blamed for raiding villages and government outposts in the area.

However worries that Isis might be expanding its operational reach heightened this week when the group claimed credit for an attack on a hospital that killed at least 74 people in the Pakistani city of Quetta. A Pakistani Taliban faction also claimed responsibility.

Khan had been reported dead before. Last year Afghan intelligence agents claimed he had been killed but the report was never confirmed.

Earlier on Friday Afghanistan’s ambassador to Pakistan, Omar Zakhilwal, told Reuters he had seen confirmation from Afghan security forces about Khan’s death. “I can confirm that Isis Khurasan [Afghanistan and Pakistan] leader Hafiz Saeed Khan along with his senior commanders and fighters died in a US drone strike on 26 July in Kot district of Afghanistan’s Nangarhar province,” he said.

Pentagon spokesman Gordon Trowbridge later confirmed Khan’s death, and said in a statement that the drone strike took place during joint operations by US and Afghan special operations forces against Isis in the southern part of Nangarhar province. Trowbridge said the airstrike was in Achin district, as opposed to Kot district.

The Taliban’s various factions in Afghanistan and Pakistan as well as their al-Qaida allies are bitter rivals of al-Baghdadi.

Taliban and Isis fighters have battled over territory in Nangarhar, though both have recently been more busy defending against US and Afghan assaults.

Between January and early August, US warplanes conducted nearly 140 airstrikes against Isis targets in Afghanistan, according to the US military.

Afghan forces, backed by the US, killed an estimated 300 Isis fighters in an operation two weeks ago, the top US and Nato commander in Afghanistan said on Wednesday, calling it a severe blow to the group.